• Journal of the Korean Ceramic Society
• /
• v.13 no.1
• /
• pp.30-34
• /
• 1976

In general the chemical composition of glass ceramics in Li2O-Al2O3-SiO2 system is similar to the composition of $\beta$-spodumene (Li2O-Al2O3-4SiO2). With the object to manufacture the glass ceramics which can be produced in the domestic pot the composition of glass was so settled at 1.0 Li2O.0.9Al2O3.6.0SiO2 in order to reduce the contents of Li2O, to prevent the corrosion of the pot and to decrease the cost of raw materials. 0.2 mole and 0.1 mole of the mixture of TiO2 and ZrO2 as nucleants were added to the basic composition of 1.0 Li2O-0.9Al2O3-6.0SiO2. Each sample was divided into two kinds with a TiO2/ZrO2 ratio of 2 to 1 and the other with a TiO2/ZrO2 ratio fo 1 to 1. Thermal expansion coefficient, the most important property of glass ceramics, was tested. The softening point and the melting point of the samples were observed by the use of a heating microscope. The results obtained were as follows. The manufacturing of glass ceramics seems to be possible in the industrial plant using the domestic pot. 1) The composition of the glass which can be melted in the domestic pot process was near 1.0 Li2O.0.9Al2O3.6.0SiO2. 2) The temperature range of crystal creation and crystal growth was between 850-94$0^{\circ}C$, and 5 hours holding the samples at the temperature range was enough to crystallize them. The major crystal was $\beta$-spdumene and there existed petalite partialy. 3) The thermal expansion coefficient fo the crystallized glass was negative. 4) The deforming point of the crystallized glass was 1435$^{\circ}C$.

• Journal of the Korean Ceramic Society
• /
• v.38 no.10
• /
• pp.936-941
• /
• 2001

The influence of the ${Al_2}{O_3}$ particle size on flaw tolerance of the $ZrO_2/{Al_2}{O_3}$ composites prepared by mixing 5.31 mol% ${Y_2}{O_3}$-4.45 mol% ${Nb_2}{O_5}$-90.31 mol% $ZrO_2$ and ${Al_2}{O_3}$ was investigated. The composites exhibited rising R-curve behavior and plateau fracture toughness of 7.9 and $8.8MPam^{1/2}$ for the additions of 20 vol% of 0.2 and $2.8{\mu}m$ ${Al_2}{O_3}$ particles, respectively. The difference in the fracture toughness resistance was attributed mainly to the grain size of tetragonal $ZrO_2$ phase in the composites, which scaled with the ${Al_2}{O_3}$ particle size.

• Korean Journal of Materials Research
• /
• v.2 no.3
• /
• pp.172-179
• /
• 1992

$Al_2O_3/ZrO_2$ composites were fabricated by pressureless sintering from commercial powders and/or nano composite powder of $Al_2O_3/ZrO_2$. The Properties of the composites such as density, strength, hardness and fracture toughness were evaluated. Microstructures and fracture surfaces ware also examined. The flexural strength remains unchanged(~640 MPa) as long as the content of commercial powders is not extreamly high, and depends on microstructures of the composites. Fracture toughness(4.3-5.3 $Mpa{\cdot}m^{1/2}$) increases with increasing content of commercial powders. Fractography shows that failure-initiating sources are 1)surface flaws resulting from machining damage, 2)crack-shaped voids formed due to $ZrO_2$ agglomeration, and 3)surface separation caused by inhomogeneous blending and by sinterability difference between nato composite powder and commercial powders of $Al_2O_3/ZrO_2$. Failure mode of the composites was mainly transgranular.

• Proceedings of the KOSOMBE Conference
• /
• v.1995 no.11
• /
• pp.131-133
• /
• 1995

• 전자공학회논문지 IE
• /
• v.49 no.2
• /
• pp.1-8
• /
• 2012

The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.11
• /
• pp.712-717
• /
• 2014

Glass ceramic has a high mechanical strength and low sintering temperature. So, it can be used as a thick film substrate or a high strength insulator. A series of glass ceramic samples based on MgO-$Al_2O_3-SiO_2-ZrO_2$ (MASZ) were prepared by melting at $1,600^{\circ}C$, roll-quenching and heat treatment at various temperatures from $900^{\circ}C$ to $1,400^{\circ}C$. Dependent on the heat treatment temperature used, glass ceramics with different crystal phases were obtained. Their nucleation behavior, microstructure and mechanical properties were investigated with differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vicker's hardness testing machine. With increasing the heat treatment temperature of MASZ samples, their hardness and toughness initially increase and then reach the maximum points at $1,300^{\circ}C$, and begin to decrease at above this temperature, which is likely to be due to the softening of glass ceramics. As the content of $ZrO_2$ in MAS glass ceramics increases from 7.0 wt.% to 13 wt.%, Vicker's hardness and fracture toughness increase from $853Kg/mm^2$ to $878Kg/mm^2$ and $1.6MPa{\cdot}m^{1/2}$ to $2.4MPa{\cdot}m^{1/2}$ respectively, which seems to be related with the nucleation of elongated phases like fiber.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.2
• /
• pp.322-329
• /
• 2009

Machinability of LAM(Laser Assisted Machining) has been studied for ceramics such as $Al_2O_3$, $Si_3_N4$ and $ZrO_2$ by $CO_2$ laser. It was possible to remove ceramics by PCBN tool because material became softening and deterioration by local laser beam irradiation. The advantage of LAM is the ability to produce larger material removal rates and tool life. But, for cutting of $Al_2O_3$ and $ZrO_2$, stage of laser power control was needed owing to thermal shock with high temperature of workpiece by laser power. And when $Si_3N_4$ was machined by LAM, $N_2$ gas spouted from surface of one cause of high temperature. Characteristics of LAM were analyzed using pyrometer, dynamometer, SEM and EDS to measure temperature of workpiece surface, cutting force, variation of machining surface and structure of lattice respectively. As the result of this study, it was found that machinability of LAM for ceramics in $CO_2$ laser and mechanism of LAM was different according to the kind of ceramics because of properties of materials.

• Korean Journal of Materials Research
• /
• v.15 no.7
• /
• pp.453-457
• /
• 2005

Piezoelectric properties of $Pb(Mn_{1/3}Nb_{2/3})O_3-PbZrO_3-PbTiO_3$ ceramics were investigated with $Al_2O_3$ content $(0.0-1.0 wt\%)$. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with $Al_2O_3$, indicating the MPB (morphotropic phase boundary) composition of tetragonal structures. The highest sintered density of $7.8 g/cm^3$ was obtained for $0.2wt\%\;Al_2O_3-doped$ specimen. Grain size increased by doping $Al_2O_3$ up to $0.3 wt\%$, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping $Al_2O_3$ up to $0.2wt\%$, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in $O^{2-}$ ion sites and the substitution of $Al^{3+}$ ions.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2005.05a
• /
• pp.106-106
• /
• 2005

• Proceedings of the KAIS Fall Conference
• /
• 2001.05a
• /
• pp.40-46
• /
• 2001

The thermal stability of $Al_2TiO_{5}$ ceramics was improved by formation of solid solution with MgO, such as $MgAl_2O_4$ spinel through electrofusion in an arc furnance, and by limitation of grain size and microcracks with $SiO_2$, $ZrO_2$ and ${\alpha}$-$Al_2O_3$. The low thermal expansion properties of $Al_2TiO_{5}$ composites show the thermal hysteresis curves due to the strong anisotropy of $Al_2TiO_{5}$. These phenomena are explained by the opening and closing of microcracks. The relation between thermal hysteresis, microstructures and sintering temperature were studied by dilatometry.